Segue 2

Segue 2 is a dwarf spheroidal galaxy located at a distance of about 35 kpc (35,000 parsecs (110,000 ly)) from the Milky Way. It is classified as a dwarf spheroidal galaxy (dSph) meaning that it has an approximately round shape with the half-light radius of about 34 pc.

Segue 2 is one of the smallest and faintest satellites of the Milky Way — its absolute visible magnitude of about −2.5 is much lower than the luminosity of the majority of globular clusters. However, the mass of the galaxy — about 550,000 stellar masses — is substantial, corresponding to the mass to light ratio of about 650.

The stellar population of Segue 2 consists mainly of old stars formed more than 12 billion years ago. The metallicity of these old stars is also very low at [Fe/H] < −2. The stars of Segue 2 were probably among the first stars to form in the Universe. Currently, there is no star formation in Segue 2.

Segue 2 is located near the edge of Sagittarius Stream and at the same distance. It may once have been a satellite of Sagittarius Dwarf Elliptical Galaxy or its star cluster.